1. Field of the Invention
Apparatuses consistent with the present invention relate to a backlight unit and a 2D/3D switchable liquid crystal display (LCD) employing the backlight unit, and more particularly, to a backlight unit having a simple structure of providing light for a left eye vision range and light for a right eye vision range to a lenticular lens sheet, and a 2D/3D switchable LCD employing the backlight unit.
2. Description of the Related Art
As technology develops, an image display device capable of displaying a more real image is needed. Accordingly, a high resolution image display device having an increased number of pixels for displaying an image has been developed, and also a three-dimensional (3D) image display device capable of displaying an image in three dimensions is under development. Thus, the 3D image display device can be applied to not only televisions (TVs), but also to various applications including medical images, games, advertisements, education, and military affairs. Thus, a greater 3D effect and experience can be obtained.
A 3D image is generated by the principle of stereo vision of both eyes. That is, since both eyes are separated about 65 mm from each other, binocular parallax occurs as the most important factor in a 3D sense. If an actual image viewed by the eyes can be input to the eyes, the 3D sense can be easily observed. For example, the 3D sense can be observed by photographing an object using two cameras having the same characteristics and separated by the distance between both eyes, and displaying a left image photographed by the left camera and a right image photographed by the right camera on the left and right eyes, respectively.
A 3D image display device that is based on binocular parallax may be an autostereoscopic type or a stereoscopic type. The autostereoscopic type that separates the left and right images and obtains a 3D image without using glasses includes a parallax barrier type, a lenticular type, an integral imaging type, and a holography type. The stereoscopic type that uses glasses includes a polarized glasses type and a shutter glasses type.
Among the 3D image display devices, as the technology for an image panel, such as an LCD, for displaying an image develops, the non-glasses type is actively being developed. FIG. 1 illustrates an example of a non-glasses type 3D image display device 1. Referring to FIG. 1, the non-glasses type 3D image display device 1 includes a backlight unit 3, an optical switch 5, a lenticular lens sheet 7, and a liquid crystal (LC) panel 9. The lenticular lens sheet 7 is an optical member in which a plurality of semi-cylindrical lenses 7a are arranged parallel to one another and extend lengthwise, that is, along a direction y in FIG. 1, in a direction perpendicular to a viewing direction of both eyes of a viewer.
The optical switch 5 includes a cell 5a for a left eye vision range and a cell 5b for a right eye vision range. The cells 5a and 5b are formed in alternating strips, and each set of cells 5a and 5b corresponds to one of the semi-cylindrical lenses 7a. The cells 5a and 5b are alternately switched between a transparent state and an opaque state, and the cells 5a and 5b are synchronized by an image signal for a left eye vision range and an image signal for a right eye vision range provided to the LC panel 9. A light for a left eye vision range and a light for a right eye vision range can alternately be transmitted toward the lenticular lens sheet 7, which allows the incident light for a left eye vision range and the incident light for a right eye vision range to proceed toward a left eye vision range OL and a right eye vision range OR of a viewer, respectively. The LC panel 9 alternately displays an image for a left eye vision range and an image for a right eye vision range. Thus, the non-glasses type 3D image display device 1 can enable the viewer to watch a 3D image by alternately providing the light for a left eye vision range and the light for a right eye vision range in synchronism with the image for a left eye vision range and the image for a right eye vision range displayed on the LC panel 9.
However, according to the non-glasses type 3D image display device 1, since the optical switch 5 that is interposed between the backlight unit 3 and the lenticular lens sheet 7 is needed, an assembly process is complicated, and a manufacturing cost of the non-glasses type 3D image display device 1 is increased. Also, a polarized switch is used as the optical switch 5, which further degrades the light use efficiency.
Since the non-glasses type 3D image display device 1 uses all pixels of the LC panel 9 to display the image for a left eye vision range and the image for a right eye vision range, the resolution of the image for a left eye vision range and the image for a right eye vision range is that of the LC panel 9. However, since the non-glasses type 3D image display device 1 needs one frame of the image for a left eye vision range and one frame of the image for a right eye vision range to display one frame of a 3D image, a decrease in a frame rate might occur. Since the image for a left eye vision range and the image for a right eye vision range cannot be instantly switched due to the limit in the response speed in the LC panel 9, when the frame rate decreases, a problem of crosstalk, in which the image for a left eye vision range and the image for a right eye vision range are mixed, becomes severe.